The Pim kinases form a distinct family of serine/threonine kinases and have been implicated as having a functional role in cell survival (Amaravadi et al., J. Clin. Invest. 115: 2618 (2005)). Pim-2 is a highly conserved serine/threonine kinase involved in cell proliferation, meiosis and the prevention of apoptosis (Baytel et al., Biochim. Biophys. Acta Gene Struct. Expr. 1442: 274 (1998)). Murine Pim-2, also known at Tic-1, has been reported to be about 53% identical in sequence at the amino acid level to the proto-oncogene Pim-1, and to be expressed at low levels in a variety of tissues, with the highest expression in the brain and thymus (van der Lugt et al., EMBO J. 14(11): 2536 (1995)). Both the Pim-1 and the Pim-2 loci are common sites of provirus integration and studies have suggested that these kinases act in a functionally redundant fashion in tumorigenesis (Haupt et al., Cell 65: 753 (1991); Bruer et al., EMBO J. 8: 743 (1989); Cuypers et al., Cell. 37: 141 (1984); van der Lugt et al., EMBO J. 14(11): 2536 (1995)). The Pim-1 proto-oncogene is believed to be one of the most potent collaborators of myc proto-oncogenes in inducing lymphomagenesis in mice (van der Lugt et al., EMBO J. 14(11): 2536 (1995)). Allen et al. (Oncogene 15: 1133 (1997)) suggest, based on proviral tagging experiments, that Pim-2 is similar in oncogenic behavior to Pim-1. They note that while Pim-1 and Pim-2 differ with respect to basal expression in tissues, both genes are highly expressed in response to the same cytokines, and they describe a Pim-2 transgene in lymphoid cells which was seen to predispose mice to T-cell lymphomas like those promoted by pim-1 transgenes. Additionally, several reports have linked abnormal expression of Pim kinases to various human cancers including prostate (Valdman et al., Prostate 60: 367 (2004)), chronic lymphocytic leukemia and non-Hodgkin's lymphoma (Cohen et al., Leuk. Lymphoma 45: 951 (2004)), and multiple myeloma (Claudio et al., Blood 100: 2175 (2002)).
As iterated above, both Pim-1 and Pim-2 genes, encode labile, cytoplasmic serine/threonine kinases. Phosphorylation of protein substrates by serine/threonine kinases is often involved in the transduction of signals from the cell surface receptors to intracellular effectors. It is believed that Pim-2, like Pim-1, is a target for gp130-mediated signal transducer and transcriptional activator 3 (“STAT3”) signaling. As is known to those of ordinary skill in the art, the activation of STAT3 by the cytokine receptor gp130 is required for both G1 to S cell cycle transition, as well as, anti-apoptosis (Shirogane et al., Immunity 11: 709 (1999)).
Baytel et al. (Biochim. Biophys. Acta Gene Struct. Expr. 1442: 274 (1998)) report cloning of the h-Pim-2 gene. In comparison to mouse Pim-2, h-Pim-2 is reported by Baytel et al. to encode a protein that shares 90% identity and 93% similarity at the primary structure level. At the RNA level, two Pim-2 transcripts have been identified in humans, a 2.2 kb transcript that is highly expressed in hematopoietic tissues and in leukemic and lymphoma cell lines, and a 5.0 kb transcript that is detectable in spleen, thymus, small intestine and colon apoptosis (Baytel et al., Biochim. Biophys. Acta Gene Struct. Expr. 1442: 274 (1998)). The Pim-2 gene in humans is believed to be X-linked (van der Lugt et al., EMBO J. 14(11): 2536 (1995)).
It has recently been disclosed (Li et al., J. Biol. Chem. 276: 18579 (2001) that Pim-2 is induced by lipopolysaccharide (LPS) in a variety of cell lines. Studies suggest that up-regulation of Pim-2 in 70Z3 cells by LPS is controlled by the IKK/NF-κB pathway. Gold et al. (J. of Immunol. 168: 744 (2002)) have recently reported that Pim-1 is a target of CD-40 signaling in B cells, and the increase in Pim-1 expression observed as a consequence of CD40 signaling was regulated via the NF-κB pathway.
Aberrant protein serine/threonine activity has been implicated, or is suspected in a number of pathologies including septic shock, bone loss, psoriasis, rheumatoid arthritis, many cancers and other proliferative diseases (See, U.S. Pat. No. 6,165,716 to Creasy et al. (Issue Date: Dec. 20, 2000)). Researchers have expended considerable time to identify serine/threonine protein kinases that may be involved mechanistically in various pathological conditions. Inhibition of such kinases may thereby be useful in the prevention and/or amelioration of various dysfunctions or diseases. For example, U.S. Pat. No. 5,972,606 to Creasy et al. discloses a human protein serine/threonine kinase, designated HOACF72, of the hYAK1 family of polypeptides, antibodies against which are said to be useful in the treatment of bone loss, inflammatory diseases such as rheumatoid arthritis, osteoarthritis, adult respiratory disease syndrome (ARDS), inflammatory bowel disease (IBD), psoriasis, dermatitis, asthma, allergies, infections, septic shock, pain, cancers, anorexia, bulimia, and a host of other conditions. U.S. Pat. Nos. 5,965,420 and 6,165,766, also to Creasy et al. (Issue Dates: Oct. 12, 1999 and Dec. 26, 2000, respectively), assert human YAK3 polypeptides and polynucleotides, antibodies against which are said to be useful for treating bone loss, inflammatory diseases, infections, immunodeficiency disorders, septic shock, pain, cancers and a host of other pathological conditions. Therefore, there is a need for identification and characterization of further members of the serine/threonine protein kinase family to identify kinases which may be involved in pathological processes. There is also a need to identify potential relationships between these kinases and disease states themselves.
The work cited above supports the principle that inhibition of Pim kinases will be beneficial in the treatment of diseases. Therefore, a need exists for small molecule inhibitors for treating these diseases with optimized efficacy, pharmacokinetic and safety profiles.
Pyrazine compounds and derivatives thereof have been disclosed in the art. WO2005058876A1 (Axxima Pharmaceuticals AG) discloses pyrazine derivatives for use in treatment of infectious diseases. WO2002060492 (Cytopia) is directed to methods of inhibiting kinases. U.S. Pat. No. 6,340,759 (Eisai) is directed to fused pyridine derivatives for use as a medicament having a serotonin antagonism.